1. Field of the Invention
The invention relates to a rotation angle detecting device that detects a rotation angle of a rotary shaft.
2. Discussion of Background
There is known a rotation angle detecting device of this type, which utilizes a resolver that outputs multiple-phase signals based on a rotation angle of a rotary shaft. The resolver includes a rotor that rotates together with the rotary shaft and a stator that is arranged so as to surround the rotor. The resolver includes an exciting winding and multiple-phase detecting windings. In the resolver, a magnetic field is formed by inputting an exciting signal to the exciting winding. The magnetic field is applied to the multiple-phase detecting windings, and thus, an induced voltage is generated in the detecting winding of each phase. Thus, sinusoidal signals having different phases are output from the detecting windings of the respective phases. In addition, when a magnetic field that is applied to output windings of the respective phases varies with the rotation of the rotor, an induced voltage that is generated in the detecting winding of each phase varies. Thus, the amplitude of the signal that is output from the detecting winding of each phase varies with the rotation angle of the rotor. The signal that is output from the detecting winding of each phase is input to a resolver/digital converter (R/D converter) via a signal line corresponding to each phase. The R/D converter computes the rotation angle of the rotor, that is, the rotation angle of the rotary shaft, on the basis of output signals of the respective phases.
In such a rotation angle detecting device, when a short circuit occurs in the signal lines of the respective phases, corresponding signals that are input to the R/D converter do not correspond to the rotation angle, and it is not possible to appropriately detect the rotation angle. Thus, in such a rotation angle detecting device, it is desirable to be able to detect a short circuit in the signal lines. A conventional rotation angle detecting device that includes such a short circuit detecting function is described in US2004/0017206 A1.
In the rotation angle detecting device described in US2004/0017206 A1, resistive elements are respectively provided in lines that respectively connect the detecting windings and signal lines of the respective phases of the resolver. Then, by setting the resistance values of the resistive elements corresponding to the respective phases to values different from one another, the median values of output signals that are output from the resolver to the signal lines of the respective phases are set to values different from one another. Thus, when a short circuit occurs in the signal lines of the respective phases, the median values of output signals of the respective phases, which are input to the R/D converter, vary on the basis of the locations of the short-circuit signal lines. Therefore, by monitoring the median values of output signals that are input to the R/D converter, it is possible to detect a short circuit in the signal lines.
In the rotation angle detecting device described in US2004/0017206 A1, it is necessary to provide the resistive elements in the resolver. Therefore, there is a possibility that the size of the resolver may increase.